Tapered thread cutting machine

ABSTRACT

A tapered thread cutting machine includes a multi-part rotary machining head, one part including a through-recess and another being a separable interior wear plate. Interacting chaser holders are mounted in the recess and include angled V-shaped slots in which block type chasers may be secured between clamps and locating pins enabling the chasers to be removed and replaced without removing the holders from the recess. The holders are driven by a linear cam for opening and closing movement through a thrust block mounted on a guide rod, such thrust block being fitted in a slot in one holder but otherwise not secured thereto so that binding in the opening and closing of tool holders is minimized.

This invention relates to a tapered thread cutting machine and moreparticularly to certain improvements in relatively small and portablethreading machines for forming external tapered thread on the ends ofbar stock and the like such as concrete reinforcing bar.

BACKGROUND OF THE INVENTION

Relatively small and portable tapered thread cutting machines findingutility in the cutting of tapered threads on the ends of bar stock suchas the steel used to reinforce concrete are currently being utilized byErico Products, Inc. of Solon, Ohio and Erico Europa B.V. of Tilburg,Holland in connection with the coupling of concrete reinforcing barsknown as the LENTON system. LENTON is a trademark of Erico Products,Inc. for both the machines for forming the tapered threads and for thecoupling system.

In such machines a rotary machining head is employed which includes arecess in its face. Within the recess which is in the form of a regularpolygon or square, tooling holders are mounted which in turn support thechasers which may be opened and closed for successive passes for theformation of the thread. A linear cam through a thrust block causesmovement of one of the chaser holders which in turn because of theircooperating configuration within the recess causes movement of all.

Because of the interaction of the tooling holder with the inside surfaceof the recess as well as a back wear plate, the surfaces thereof must bemachined and finished to a substantial degree of precision to avoidbinding or chattering during the movement of the parts and to preventexcessive wear.

The rotary machining head is normally formed from a single large castingwith the recess being formed therein by an end mill operation. After therecess is formed the back wear plate is normally press fit into therecess thus formed. Because of the end mill operation which necessarilyentails tooling or spindle deflection, and the press fit operation, theprecision of formation of the inside surfaces of the recess and the wearplate, when assembled within the recess, cannot be ensured. Furthermore,the balance of the rotary machining head which is connected to thetransmission is unnessarily massive and heavy when utilizing a one-piececasting.

Further contributing to binding is the employment of the cam thrustblock which is fastened to one of the holders and which is held againstthe linear cam by a spring which seats against the back of the thrustblock. This type of design may tend to create an eccentic loading whichis tranferred from the thrust block to the associated tool holderfurther creating binding in the movement of the tool holders whichcauses problems in both the opening and closing, and particularlyclosing of such holders.

Furthermore, prior art tool holders and the chasers supported therebyare unnessarily complex with the chasers fitting in recesses or openingsin the tool holders and requiring disassembly of the tool holders fromthe recess to replace the chasers. Moreover, the special chasersrequired to fit the tool holders are of complex shapes requiring amultiplicity of machining and grinding operations making the wearreplacement chasers unduly expensive to manufacture in addition to theproblem of disassembly for replacement.

Reference may be had to Canadian Pat. Nos. 1,101,617 and 1,108,357 foran illustration of some types of prior art threading machines.

SUMMARY OF THE INVENTION

With the present invention a multi-part rotary machining head isprovided which is formed primarily in three parts. One part includes therecess which is formed as a through-recess in that part enabling theinterior wall to be formed to a considerable degree of precision. Thesecond part is the wear plate which closes the interior end of therecess and a third part is the remaining portion of the rotary machininghead connected to the transmission which may be of lighter weightmaterial. The three parts are assembled enabling the formation of therecess and the interior wear plate in a precise relationship heretoforeunobtainable. In this manner, the recess does not have to be formed byan end mill subject to tooling or spindle deflections nor does the wearplate require to be press fit into the recess.

The opening and closing of the tool holders is obtained throughutilization of a cam thrust block which is mounted on one of the toolholders without a fastener and in a slot with a tight fit, but which hassome play for insertion and removal. The cam thrust block is in turnmounted on a guide pin or rod which goes completely through the thrustblock and through a spring. The spring is captured by a head on the rodand a removable plug in turn captures the head. This construction hasbeen found to minimize binding or chattering in the adjustment formovement of the tool holders.

With such construction, it has also been found that a more simplifiedchaser design and associated tool holde may be provided. The chaser maybe formed in a much more economical manner simply by cutting essentiallyrectangular blocks from elongated chaser stock and then surface grindingor relieving the cutting edges. Moreover, the chaser may be held in thetool holder in a relatively simple angled V-shaped slot between a stoppin and an adjustable clamp. The adjustable clamp exerts a component offorce to hold the chaser against the walls or the back of the slot andagainst the stop pin. The construction of each tool holder isessentially the same. However, the stop of each successive tool holdermay be axially offset from the stop of the next holder by the reciprocalof the number of chasers employed times the pitch of the thread beingcut. In any case the chasers may much more economically be formed andmay be removed and replaced without disassembly of the tool holder fromthe recess.

It is accordingly an important object of the present invention toprovide such tapered thread cutter wherein the rotary machining head orblock is formed of a multiplicity of parts, one part forming theinterior walls of the recess and being open at both ends when formed topermit the interior walls to be formed to a precise planarity andrelationship to each other.

Another important object is the formation of such rotary machining headwherein the wear plate is formed separately and does not require to bepressed through the recess for assembly.

Another such object is the provision of such rotary machining headwherein the balance of the head connecting the same to the transmissionmay be made of a lighter weight material.

Also an important object is the provision of such cutter wherein one ofthe holders within the recess includes a projecting cam thrust blockthrough which a guide rod extends parallel to the movement of the holderwith spring means surrounding the guide rod urging the thrust blockagainst a control cam.

Still another important object is the provision of such thrust blockwhich is mounted in a recess in the holder from which it projects but isotherwise unconnected to the holder.

A further important object is the provision of such cutter wherein thechaser holders include on their interior an angularly disposed recesswith a stop at one end of the recess and a clamp at the other endoperative hold a chaser in the recess.

It is also an object of the invention wherein the recess is a V-shapegroove on the interior of the holder and wherein the clamp includes acomponent of force seating the chaser into the groove and against thestop.

It is also an important object of the present invention wherein thechasers can readily be manufactured in the form of rectangular blocksand secured in and removed from the holders without requiringdisassembly or removal of the holders from the head recess.

These and other objects and advantages of the present invention willbecome more apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described in thespecification and particularly pointed out in the claims, the followingdescription and the annexed drawings setting forth in detail certainillustrative embodiments of the invention, these being indicative,however, of but a few of the various ways in which the principles of theinvention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

In said annexed drawings:

FIG. 1 is an exploded view of the rotary machining head, tool holdersand chasers of a prior art LENTON machine;

FIG. 2 is a similar exploded view illustrating the improvements of thepresent invention;

FIG. 3 is an enlarged fragmentary transverse section of the rotarymachining head through the cam thrust block and its associated guide pinor rod as taken from the line 3--3 of FIG. 2;

FIG. 4 is an fragmentary view partly in section of such head taken fromthe line 4--4 of FIG. 3;

FIG. 5 is an enlarged view of a tool holder taken from line 5--5 of FIG.2;

FIG. 6 is a front elevation of the tool holder seen from the line 6--6of FIG. 5; and

FIG. 7 is a somewhat schematic plan view of the rectangular stock fromwhich the block form chasers may be cut for finish grinding.

DESCRIPTION OF THE PRIOR ART

Referring first to FIG. 1, there is illustrated a rotary machining headblock 10 which is normally formed of a single steel casting. The blockis mounted in the machine with its drive for axial reciprocation in thedirection of the arrow 11 with the end 12 of the block being connectedto the drive transmission while the opposite end 13 is provided with arecess 14. The recess is shown in the form of a square and closed at itsinner end by a wear plate 15 which is normally pressed through theopened end of the recess.

Fitted within the recess 14 are four relatively complex tooling holdersseen at 18, 19, 20 and 21, such that movement of one tool holder whenwithin the recess moves all tool holders for opening and closingmovement.

One of the tool holders shown at 18 is provided with an exterior recess23 which seats a cam thrust block 24 held thereto by fastener 25. Thecam thrust block projects upwardly in the assembled condition of thetool holders through substantially radial slot 27 in the head 10 whichintersects with the linear exterior axial slot 28. Mounted within theaxial slot 28 is a control key or cam 30 which includes a linear camsurface 31 on the underside thereof which abuts against the upper edge32 of the cam thrust block 24. In order to maintain the thrust block andthe chaser holder against the control surface of the cam there isprovided springs 34 and 35 trapped in hole 36 between the threaded plug37 and seat 38 in the face of the cam thrust block opposite the camengaging surface 31.

Movement of the control cam 30 is obtained by axially spaced rollers 40and 41 held in place by shoulder bolts 42 and 43, respectively. Therollers 40 and 41 are positioned on opposite sides of an axiallyadjustable control ring 44 shown fragmentarily in FIG. 1.

Adjustment of the ring 44 is employed initially to contact the roller 40to move the cam or key to a starting position which closes the holders apredetermined amount. A control setting is employed for this purpose.This setting establishes the amount of metal to be removed for the pass.When the rotary head 10 indexes forwardly or toward the viewer in thedirection of the arrow 11 roller 41 engages the ring 44 initiating theuniform opening of the holders by a linear angled portion of the cam(the same as the taper being cut). In this manner, each chaser has auniform depth of cut for each pass. At the end of the pass the cam isprovided with a portion which opens the holders permitting the cam to bereset for the next pass. The number of passes employed may of coursedepend upon the diameter of the bar being threaded.

Also, as seen in FIG. 1, each chaser holder is provided with a majorslot 46 in which the chaser 47 is inserted in the direction of thedoubleended arrow 48. One edge of the slot is closed by a chaserclamping plate 49 secured by fasteners 50 to the chaser holder. Thelateral edges of the clamping plate 49 are provided with flanges fittingwithin the flange recesses illustrated. The extent to which the chaseris inserted in the holder may be controlled by a stop pin which engagesa finished flat 53 or by a threaded stud engaging a shoulder on thechaser.

In normal practice, to remove a chaser 47, the tool holders 18 through21 must normally be removed from the recess 14. The chaser clampingplates 49 are then loosened and the chasers are then pulled from theholders in the direction of the arrow 48. Also, care must be taken toreplace the chasers and holders in a precise order. It can be seen thatthe chasers cannot be pulled from the assembly in the manner indicatedwhen the holders are in the recess because of the close fit andrelationship therebetween.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIGS. 2, 3 and 4, it will be seen that the rotarymachining head shown generally at 60 is formed of three separate pieceswhich may be termed a machining head 61, a wear plate 62 and a machininghead extension 63.

The machining head 61 is provided with a square through-recess 64.Because the recess 64 is a through-recess, it need not be formed with anend mill subject to spindle or tool deflection. In this manner, theplanar walls 65, 66, etc. may be formed precisely at right angles toeach other and precisely in planes parallel to the axis of the rotarymachining head 60. Since the tool holders are designed to slide withinthe precise interior walls of a true square box, the formation of therecess in this manner itself minimizes binding, chattering, or excesswear which might otherwise occur. The wear plate 62 which forms theinterior wall of the recess 64 may be formed with flat opposite facesand may be secured or clamped between the head 61 and head extension 63against a flat surface 68 forming the rear of the machining head toensure that the interior face of the recess 69 is normal to the axis ofthe assembly. Press fitting such a wear plate into the open end of arecess in a one-piece machining head cannot assure the normality andplanarity of the wear plate as with the present invention. The wearplate, of course, forms a wear surface for the chaser holders. Themachining head extension 63 which forms the larger volume of the rotarymachining head assembly may rather easily be formed from a lighterweight material such as aluminum thus significantly reducing the totalmass of the rotary assembly while still obtaining the precision of thebearing and wear surfaces for the chaser holders. The plate 62 and theextension 63 are formed with aligned center holes for the stock andcutting oil.

As seen perhaps more clearly in FIG. 4, the machining head extension 63on its forward end has a peripheral skirt 70 which encloses theperiphery of the wear plate 62 and which seats against a shoulder 71 onthe rear of the machining head 61. The parts of the machining head maybe assembled with the assistance of one or more dowl pins 72. Each ofthe three major components of the assembly include aligned slots seen at74, 75 and 76 to receive the control key or cam 77.

As in connection with the prior art there may be four chaser toolholders and respective chasers situated within the recess 64 slidingagainst each of the planar interior walls. The chaser tool holder 80adjacent the cam 77 is provided with an exterior axial slot 81 in whichthe interior extension 82 of cam thrust block 83 is fitted. The camthrust block 83 is provided with a transaxial through-hole 84 andoptionally may include a top removable wear insert 85 designed to bearagainst the linear interior cam surface 86 of the control key or cam 77.When assembled with the chaser tool holder 80, the cam thrust block 83fits upwardly through the transaxial slot 88 intersecting slot 74. Theintersecting slot accomodates the cam thrust block 83 for movementtransversely of the slot 74 and of course the control cam surface 86.The thrust block 83 is mounted on a hardened support pin or guide rod 90which includes a head 91. The rod 90 fits closely through hole 84 in thecam thrust block. A spring 93 fits around the pin 90 between the thrustblock and head 91 and the entire assembly is captured in hole 94 bythreaded plug 95.

Referring now to FIGS. 5 and 6 in addition to FIGS. 2 and 3, it will beseen that the square recess 64 is designed to accomodate fourinteracting tool holders with only the two opposite tool holders beingshown in FIG. 2. In FIG. 2, the opposite tool holder 98 is shown withits chaser 99 removed. The chaser 100 of the tool holder 80 is shownassembled. Since the tool holders are essentially the same, only thetool holder 98 seen in detail in FIGS. 5 and 6 will be described. Thetool holder 98 is essentially in the form of a triangular block with theapex relieved as well as one corner along the base or interior faceremoved. Thus, the tool holder 98 includes an inner surface 102 formingthe base of the triangular block and two outer faces 103 and 104 whichare at right angles to each other. The face 103 of the tool holder formsa guide face guiding the tool holder along the wall 66 of the recess.The apex of the triangular block is relieved between the surfaces 103and 104 as seen at 105 to provide clearance for the rounded corners ofthe recess. The corner at one end of the base or inner surface 102 maybe slightly relieved as seen at 106 while the opposite end of the blockat the base is provided with a guide surface 107 which is at rightangles to the inner face or base 102. The guide surface 107 ridesagainst the inner face of the adjacent tool holder.

As seen more clearly in FIG. 5, the block is provided with an inner endface 109 and an outer end face 110. Both end faces are at right anglesto the other major faces. The inner end face 109 rides against the wearplate 62 and thus it is important that the wear plate be perfectly flatand that the inner walls of the recess also be perfectly flat and atright angles not only to each other but also to the wear plate. Theouter end face 110 rides against the cover plate secured to the face orfront of the machining head 61.

The inner face 102 of each tool holder block is provided with a V-shapegroove seen generally at 114. The walls 115 and 116 of the V-shapegroove may be at right angles to each other but the apex of the grooveor inner corner 117 extends at an angle to the axis of the machine equalto the angle of taper of the thread to be generated on the workiece.Thus, as viewed in FIG. 6, the wall 116 of the slot extends at a slightangle downwardly while the wall 115 extends at a somewhat more severeangle outwardly. It is this slot 114 in which the chaser 99 ispositioned and held. Chip clearance reliefs may be provided adjacent theslot 114 as indicated 120 and 121 with the latter clearance even beingfurther relieved by the clearance 122.

The associated chaser 99 is in the form of a substantially rectangularblock and is clamped in the slot 114 by a clamp screw 124 passingthrough a dished or spring washer 125 and into a tapped blind bore 126in the face 110 of the holder. Such face is circularly relieved asindicated at 127 so that when the clamp screw is seated in clampingarrangement with the chaser its head will clear the end face 110. Asseen more clearly in FIG. 6, the circular relief intersects one end ofthe V-shape slot 114 so that the dished washer and head bear against anend of the chaser 99. The clamp screw clamps the chaser against a stopor locating pin 130 which is positioned in blind bore 131 in the face116 of the slot 114. It should be noted that axis 133 of the clamp screw124 and its associated tapped bore is normal to the end faces 109 and110 of the tool holder while the surfaces 115 and 116 are not. Thus, theclamping force on the end of the chaser exerts a component of forceurging the chaser against both surfaces 115 and 116 in addition toclamping the chaser against the stop pin. The axis of the blind bore 131is parallel to the end faces 109 and 110.

Referring now to FIG. 7, it will be seen that the chasers may readilyform from tool steel bar stock shown generally at 135 which isrectangular in section. On the top surface there may be milled theleading edge chamfers seen at 136 and the thread form cutters 137. Afterthe bar stock is properly milled it may be cut along the lines indicatedat 138 to form the chaser blanks. The cutting edges may then be groundto form the necessary reliefs while the opposite edge is maintained as aright angle corner properly to seat in the slot 114 of the respectivetool holder.

If the chaser bar stock is also subsequently milled or finished toprovide the required leading edge chamfers the chaser for each toolholder may be formed from the same bar stock with the only difference inthe holder being the spacing of the locating pin 130. In this manner,the locating pin of successive tool holders would be spaced thereciprocal of the number of tool holders times the pitch. If thelocating pins for each tool holder are the same, then the chaser barstock for the respective tool holders may be formed in essentially thesame manner, but with leading edge chamfers and thread cutting sectionspositioned on different bar stock. In either event, the chasers may beformed of relatively simply rectangular bar stock and cut intosubstantially rectangular blocks for subsequent finishing for insertionin the required tool holders.

With the present invention, the multi-piece rotary machining head avoidsprior art problems finishing the interior surfaces of the recess againstwhich the tool holders must move. The same is true of the interior wearplate. Moreover, in association therewith, the mounting of the camthrust block on the associated tool holder without fasteners in a slotwith a tight fit, but which has some play for insertion and removal, incombination with the mounting of such block on a rod which goes throughthe block, prevents cocking of the cam thrust block and if any doesoccur, it is then absorbed by the non-fastened connection between theblock and holder. The multi-part construction of the rotary machininghead enables the surfaces against which the chaser tooling holders rideto be much more precisely formed, the balance of the rotary machininghead being of a lighter weight material reducing the energy requiredboth to drive the unit and to form it.

In addition, the chasers and tool holders of the present invention areof a much more simplified construction. The chasers may be formedeconomically from tool steel bar stock and may either be formed suchthat the tool holders and the associated clamping screws and stops areidentical or such that the tool steel stock be slightly modified and theposition of the stop pin against which the chaser is clamped may bemodified for each tool holder by the reciprocal of the number of toolholders times the pitch. The construction and formation of the chasersand of the associated tool holders is greatly simplified permittingchaser removal and replacement without removal and disassembly of thetool holders from the recess of the head.

Although the invention has been shown and described with respect to apreferred embodiment, it is obvious that equivalent alterations andmodifications will occur to others skilled in the art upon the readingand understanding of this specification. The present invention includesall such equivalent alterations and modifications, and is limited onlyby the scope of the claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A tapered thread cutterfor bar stock, tubing and the like comprising a rotary head blockincluding a polygonally shaped recess supporting chaser holders onrespective interior facets thereof for opening and closing movement,each chaser holder including on its interior a V-shape groove angularlydisposed with respect to the rotational axis of said head block andhaving the walls thereof at right angles to each other, a stop at oneend of said groove, and a clamp near the other end operative to hold achaser in said groove, said chaser being an essentially rectangularblock having substantially parallel faces with right angle sides injuxtaposition with the sides of said V-shape groove.
 2. A thread cutteras set forth in claim 1 wherein said clamp includes a component of forceseating the chaser in said groove.
 3. A thread cutter as set forth inclaim 1 wherein each stop is axially offset from the stop of the nextchaser holder by the pitch of the thread being cut times the reciprocalof the number of chaser holders employed.
 4. A thread cutter as setforth in claim 1 wherein each chaser is cut from an elongate rectangularblock after thread cutting teeth are formed in one planar surfacethereof.
 5. A thread cutter as set forth in claim 1 wherein the apex ofsaid groove extends at an angle to the axis of the head block equal tothe angle of taper of the thread to be generated on the work piece.
 6. Athread cutter as set forth in claim 1 wherein said clamp, groove andstop permit securement of said chaser in the chaser holder withouthaving to remove the chaser holder from the recess. pg,20
 7. A threadcutter for bar stock, tubing and the like comprising a rotary head blockincluding a polygonally shaped recess in one end adapted to receive andguide a set of tool holders for opening and closing movement, said headblock being substantially formed of three parts, one part havinginterior walls forming the recess which is open at both axial ends ofsaid one part when formed to permit the interior walls thereof to beformed to a precise planarity and relationship to each other, a secondpart in the form of a removable wear plate having a planar finishedsurface, and a third part forming the balance of said rotary head block,said third part being made of material lighter in weight than said onepart, and means for securing together said one and third parts with saidremovable wear plate clamped therebetween at least partially to closeone end of said recess with said finished surface.
 8. A thread cutter asset forth in claim 7 wherein said one part includes a peripheralshoulder while the balance includes a peripheral skirt adapted to fitwithin said shoulder fully enclosing said plate.
 9. A thread cutter asset forth in claim 7 including a projecting cam thrust block operativeto move one of said tool holders, a guide rod extending through saidthrust block parallel to the movement of said one tool holder, andspring means urging said thrust block against a control cam.
 10. Athread cutter as set forth in claim 4 wherein said thrust block isengaged in a recess in said one tool holder but is otherwise unconnectedto said one tool holder.
 11. A thread cutter as set forth in claim 9including a shoulder or head on said rod, said spring means extendingbetween said shoulder or head and cam thrust block.
 12. A thread cutteras set forth in claim 7 including means to secure a tool in each saidtool holder without requiring removal of the tool holder from therecess.
 13. A thread cutter as set forth in claim 12 wherein each toolholder includes on its interior an angularly disposed V-shape groovewith a clamp adjacent one end and a stop adjacent the other.
 14. Athread cutter as set forth in claim 13 wherein each clamp includes acomponent of force seating the tool in said groove.
 15. A tapered threadcutter for bar stock, tubing and the like comprising a rotary head blockincluding a recess in one axial end adapted to receive and guide a setof tool holders for opening and closing movement, one of said holdersbeing movable by a cam thrust block projecting therefrom, a guide rodextending through said thrust block parallel to the movement of theholder from which the thrust block projects, a control cam operative tomove said thrust block, and spring means urging said thrust blockslidably along said guide rod against said control cam.
 16. A threadcutter as set forth in claim 15 wherein said thrust block is engaged ina recess in the holder from which it projects but is otherwiseunconnected to said holder.
 17. A thread cutter as set forth in claim 16including a shoulder or head on said rod, said spring means extendingbetween said shoulder or head and cam thrust block.
 18. A tapered threadcutting machine comprising a rotary machining head including a recesshaving planar interior walls, each parallel to the axis of the head, aplurality of tool holders in said recess engaged with said walls andeach other for opening and closing movement along said walls in responseto movement of one of said holders without binding, a projecting camthrust block operative to move said one tool holder, said thrust blockbeing linearly slidably supported on a relatively fixed guide rodextending parallel to the movement of said one tool holder, a controlcam operative to bear against said thrust block to move said thrustblock along said guide rod to effect opening movement of said toolholder, and means to secure a tool in each tool holder.
 19. A threadcutter as set forth in claim 18 wherein each tool holder includes on itsinterior an angularly disposed V-shape groove with a clamp at one endand a stop at the other.
 20. A thread cutter as set forth in claim 19wherein each clamp includes a component of force seating the tool insaid groove.
 21. A thread cutting machine as set forth in claim 18including spring means urging said thrust block against said controlcam.
 22. A thread cutter as set forth in claim 21 wherein said thrustblock is mounted in a recess in said one tool holder but is otherwiseunconnected to said one tool holder.
 23. A thread cutter as set forth inclaim 22 including a shoulder or head on said rod, said spring extendingbetween said shoulder or head and cam thrust block.
 24. A thread cutteras set forth in claim 18 wherein said rotary machining head is formed ofat least two parts, one part forming the interior walls of the recessand being open at both ends of the recess when formed to permit theinterior walls to be formed to a precise planarity and relationship toeach other.
 25. A thread cutter as set forth in claim 24 including aremovable plate secured to said one part and at least partially closingone end of said recess with a hardened finished surface.
 26. A threadcutter as set forth in claim 25 wherein the balance of the rotarymachining head is a third part.
 27. A thread cutter as set forth inclaim 26 wherein said third part is a lighter weight material.